Lens regeneration during adulthood is a unique phenomenon restricted only to some urodeles. Once the lens is removed the new lens is regenerated from the dorsal iris pigmented epithelium by transdifferentiation of these cells to lens cells. This event takes place only from the dorsal but not from the ventral iris. However, as has been shown by culturing eye cells, the ability of pigment epithelium, lens epithelium or retina from a variety of species, including old human, to transdifferentiate to lens in vitro is retained. Furthermore, the ventral iris pigmented epithelium is also capable of differentiation in vitro. Since the culturing of cells involves cell dissociation and adhesion, regulation of molecules involved in these processes should be an important element. The ability of only the dorsal iris to regenerate to lens in vivo also implies strongly spatial regulation. Homeo box- and pax-containing genes, are known to code for regulatory molecules involved in pattern formation, differentiation and axes specification. These properties make these genes good candidates for controlling events that are regulated in a spatio-temporal manner, lens regeneration being one of them. In addition, a pax-containing gene has been implicated in the eye disease aniridia. We propose to clone these genes from the eye tissues that undergo regeneration and examine their expression during the in vivo and in vitro differentiation of cells into lens. We intend to clone these sequences by means of the Polymerase Chain Reaction (PCR). The expression will be studied by in situ hybridization, Northern analysis or PCR. Such studies will provide molecular tools to study gene regulation in the eye and help fathom the basic molecular mechanisms underlying lens regeneration and transdifferentiation of the eye cells.